Conventional ionization detector types are known to include a helium ionization detector which typically operates by operating a beta particle emitter in a helium-filled ionization chamber. In the presence of helium, a characteristic emission of primary electrons, photons, and helium metastables will occur. A sample fluid that contains an unknown analyte is directed into the ionization chamber such that the analyte of interest may be ionized. Both the helium metastables and the photons are found to play a role in ionization of the analyte of interest. The magnitude of the ionized analyte molecules is manifested as a current that can be measured to ascertain the composition of one or more components in the analyte.
However, ample shot noise and avalanche effects have been observed in the typical helium ionization detector, due to a sufficient amount of secondary ionization that occurs in the ionization chamber as a result of direct interaction of the primary electrons, helium ions, and beta particles with the ionizable molecules in the analyte. As a result, the response of this detector is non-linear and subject to overloading (i.e., extreme peak heights). The helium ionization detector has accordingly been regarded as limited in its usefulness. The factors for this characterization include the stringent requirements for high-sensitivity operation, variations in response for selected species coupled with a lack of understanding of the conditions that generate such responses, and the belief that the detector is primarily suited for the analysis of gases that can be separated on low-bleed adsorption columns. See, for example, Ramsey and Andrawes, "The Modern Helium Ionization Detector", in Detectors for Capillary Chromatography, Hill, H. H. and McMinn, D. G., eds., John Wiley & Sons, 1992.
Although the design of ionization detectors continues to be an object of study in the prior art, there nonetheless exists a particular need for an ionization detector having a detector response that exhibits an improved dynamic range, lower minimum detectable level, and greater stability.